Total hip arthroplasty is often used to restore function to a diseased or injured hip joint. Positions and directions relative to the hip joint may be described in terms of proximal being nearer the hip joint, distal being further from the hip joint, anterior being nearer the front of the body, posterior being nearer the back of the body, medial being nearer the centerline of the body, and lateral being further from the center line of the body. In total hip arthroplasty (FIGS. 1-2), the articular surfaces of the femur and pelvis are cut away and replaced with prosthetic implant components. In a typical case, the implants include a hip stem component 10, a femoral head component 12, an acetabular component 14, and bone cement 16. The hip stem component includes a stem portion 18 extending down into the intramedullary canal 20 of the femur 22 and a neck portion 24 extending away from the femur 22 to support the femoral head component 12.
The femur 22 is prepared by reaming the intramedullary canal 20 down into the bone along an axis 26 from a proximal position near the hip joint at the upper end of the femur 22 toward a distal position nearer the knee joint at the lower end of the femur 22. The pelvis 28 is prepared by reaming the acetabulum 30. Bone cement 16 is introduced into the prepared intramedullary canal 20 and acetabulum 30 and the prosthetic components are seated in the bone cement 16 so that it hardens around and locks the components in place. Positioning the hip stem component 10 in the correct orientation within the cement 16 is important for proper biomechanical functioning and long term stability. It is desirable to have a uniform and strong cement mantle 16 proximally around the anterior 34, lateral 36, and posterior 38 portions of the stem component 10. Proper placement further results in appropriate loading of the implants. Hip stem components, especially collarless ones, are sometimes placed at the wrong angle in the mediolateral direction. The typical situation is a varus placement in which the angle between the neck 24 and femoral axis 26 is too shallow. Hip stem centralizers have been proposed that are implanted in the cement mantel between the hip stem component and the intramedullary canal. These prior art centralizers necessitate the expense of an additional implantable component and reduce the contact area between the bone cement and the hip stem component.